Q. If I am the tenth at a mincha minyan, but I’ve already davened mincha, what do I do at this one? I assume I don’t say Shemoneh Esrei again, but I do say Amein to all brachos. Do I say Modim d’Rabbanan? Do I say Tachanun? Do I say Aleinu? Is there anything else I should or shouldn’t do?

A. Anyone listening to a properly recited brocho should answer baruch hu ubaruch shemo followed by amen (Mishna Berura 124:22-23). One should also answer modim derabanan as well as kedusha, kaddish and barchu including reciting alenu together with the tzibur.
Although some Poskim disagree, (See Beis Avi O. H. 3: 6), Horav Shlomo Miller’s Shlit’a opinion is that one does not repeat tachanun.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a